Infrared Analysis of Photolytically Aged Biomass Burning Organic Aerosol

Abstract:

Research regarding biomass burning organic aerosol (BBOA) has been increasing in importance as the frequency and magnitude of wildfires have also increased. The emissions of wildfires can travel thousands of miles, impacting local and regional air quality. As a result, BBOA has an important role in atmospheric chemistry and radiative forcing. BBOAs have complex compositions, contributing to gaps in our understanding of how the properties of BBOA evolve as they are chemically aged in the atmosphere. In this study, we characterize the influence of photo-aging on the composition of BBOA to much longer timescales than most previous photochemical aging experiments. BBOA, derived from the burning of various biomass fuels and collected on Teflon filters, were photolytically aged using xenon arc lamps over a timeframe of up to ~3.5 days. Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR) and Offline-Aerosol Mass Spectrometry (AMS) were used to measure the chemical changes in the filters and the aqueous sample extracts to evaluate how those changes can relate to the specific fuel type. This study finds an overall decrease in the nitro group (-NO2) compounds and a shift of the -OH stretch toward higher wavenumbers, in the samples with irradiation. The mass spectral data show an increase in the average carbon oxidation state. Several unique chemical characteristics were observed for some samples, which can possibly relate to their individual fuel type. Observed changes demonstrate the rates of photo-bleaching that can occur in BBOA from different fuel types when photolyzed as dry particles over ~3.5 days.